v4l2bufferpool: set video alignment of video meta

need apply video alignment info on video meta, downstream element can get buffer alignment from video meta.

gst-launch-1.0 videotestsrc ! video/x-raw,format=YUY2,width=1920,height=1080 ! v4l2h264enc ! v4l2h264dec ! queue ! imxvideoconvert_g2d ! waylandsink

See above pipeline, the alignment of height on our platform is 16pixels, so decoder output buffer's size is 1920x1088, but output videoinfo and videometa are 1920x1080, So the alignment didn't pass downstream and cause some alignment issues when do videoconvert by g2d.